Large scale penetration of renewable energy sources, such as wind and solar energy, into an electric grid is complicated by the substantial hourly, daily, and seasonal fluctuations of such energy sources. Energy storage systems can mitigate these fluctuations by storing excess off-peak energy for use at peak-demand times. Compressed Air Energy Storage (CAES) is one example of a storage technology and can store a large amount of energy at an economical cost. Although conventional CAES systems are operational, they do suffer from low overall efficiency due to the significant amount of energy lost during the air-compression process in the form of waste heat. The Adiabatic CAES design can improve the economics of a conventional CAES system by storing the heat of compression and using it to heat the compressed air prior to the expansion process and electricity generation. However, this design is challenged by the technical complexity of the heat storage system due to the high pressures and temperatures of the compressed air. Isothermal CAES is another proposed design that focuses on improving the efficiency of CAES by close-to-isothermal compression and expansion processes. Coupling conventional CAES facilities with simple cycle gas turbine plants in various configurations for enhanced heat recovery has also been proposed to improve the storage efficiency of CAES facilities.
CAES systems are usually considered for storage requirements of tens of megawatts (MW) of electric power and hours of discharge time. There are at least two commercial CAES facilities presently in operation. The first facility located in Huntorf, Germany, can store up to 310,000 cubic meters (m3) of compressed air at a pressure range of 48-66 bar in two salt caverns and can produce 290 MW of electricity at full capacity for four hours. The McIntosh plant is the second commercial CAES facility and is located in Alabama. The McIntosh plant generates 110 MW of electricity at full capacity for 26 hours and can store up to 560,000 m3 of compressed air at a pressure range of 45-74 bar in a salt cavern.